Generally, the invention relates to the field of computer memory backup devices which have standardized computer tape cartridges. More specifically, the invention focuses upon techniques for ascertaining the appropriate placement of such cartridges to allow operation of the computer memory backup device.
Since the advent of programmable information processing systems or computers, the need to store information has grown dramatically. This information storage is frequently accomplished through devices which interconnect with the computer and act relatively independently in response to signals received from the main data processing functions of the computer. These devices, known as peripheral devices, act to receive data from the main computer memory and then to store such data on a separate media within the peripheral device.
One of the aspects of typical memory devices and computer systems is their volatility--they can unintentionally loose their contents occasionally. To overcome this limitation, backup devices have evolved. Such devices serve the simple function of separately storing large amounts of data on relatively non-volatile media. In the field of these specialized devices, the use of magnetic tape media has greatly eclipsed all other types of uses. This use is so broad that magnetic tape cartridges for computer backup devices have been designed. Such cartridges specifically meet the needs of computer users in a standardized manner.
The present invention focuses upon standardized magnetic tape cartridge systems, such as are frequently used in computer tape backup systems. The American National Standards Institute defines "magnetic tape" as tape that "accepts and retains magnetic signals intended for input/output and storage purposes for information processing and associated systems." The "standardized" magnetic tape cartridge ensures that the use of the tape cartridge for computer memory backup will be optimal, as opposed to other types of media systems which might require accommodation of existing designs.
In many computer peripheral memory devices, it is desirable to utilize media which can easily be removed and reinserted, thus allowing the user to greatly expand the memory capacity associated with the computer simply by purchasing additional media in the form of disks or tapes. While each of these different types of media have unique advantages, one need runs throughout, namely the need to sense the presence of such media before operating the peripheral device. Unlike other types of mechanisms which utilize removable media such as VCRs and audio cassette players, the need to appropriately sense the presence of memory media is particularly acute when such media is used in conjunction with a computer because of the way data interface and control standards have evolved. It should be understood that within the field of removable memory media, the inventions which have been directed to video cassettes, audio cassette tapes, and other non-computer related devices deal with entirely different circumstances. For this reason, the techniques or lack thereof involved in devices unrelated to computer backup memory storage are not viewed as particularly relevant to the problems encountered in the field of computer memory storage devices which use standardized computer tape cartridges for backup purposes.
As mentioned earlier, the need to sense the presence of the memory media before operating the tape backup device is very important. In most instances a physical act is required to trigger such sensing. This physical act can occur in a variety of manners. The user can be required to take the act or the physical act can be taken by the presence of the media itself such as when the media triggers a switch or forces a mechanism to engage it internally. While the vast majority of each of these types of system have available to them interconnections or other failsafe mechanisms to avoid an inappropriate indication, the mere fact that mechanical movements or switching is often required is a significant drawback. While those skilled in the art are generally aware that such mechanical devices are susceptible to failure, the strong desire within the computing industry to adhere to standards which allow for interconnectibility and consistency of media from one manufacturer to another has acted to direct those skilled in the art away from more appropriate solutions to the problem which are unencumbered by the limitations of the existing devices.
The standards promoted within the computer tape backup industry serve as an example of the way such standardization has directed those skilled in the art away from the approach of the present invention. The standards promoted by the American National Standards Institute (ANSI) implicitly advocate the need for cartridge-in sensing through some type of mechanical device. While the limitations of such a technique have been well known by those skilled in the art, the pervasiveness of adherence to the standards has caused those to focus on making such mechanical sensing more reliable and less expensive to manufacture rather than to simply question the desirability of using a mechanical sensor in the first place. This is dramatically evident from the fact that in the same standard which implicitly provides for mechanical sensing of the cartridge-in determination, other, non-mechanical, sensing techniques are used for other purposes. Even though these techniques are readily available to those skilled in the art, the direction in the standards acts to teach those away from the solution of the present invention and to ignore potential solutions which were already utilized in the same device. In this regard, it is also true that the relative ease with which a mechanical determination could be accomplished and the minimal expense involved caused those skilled in the art of the present invention to develop preconceived notions that alternative solutions--while perhaps overcoming limitations of existing devices--would outweigh those advantages in their difficulty and expense of implementation.
Among the aspects well known to be desirable are issues relating to reliability and minimizing energy consumption. As to the first, reliability, those skilled in the art of determining the presence of a standardized magnetic tape cartridge in a computer memory backup device have long felt the need to achieve better performance. The American National Standards, however, have served to direct them away from the solutions discovered by the present invention even though the implementing arts have long been available. This was perhaps due to the fact that while those skilled in the art recognize the need for increased reliability, they failed to appreciate that one element of the problem lay in focusing upon using available optical sensing means to determine the presence or absence of a magnetic tape cartridge. Instead the specification implicitly, and other references explicitly have acted to teach away from the direction taken by the present invention. Those skilled in the art simply did not expect such advances to be possible without modification of the existing cartridges--and therefore the ANSI standards.
In sharp contrast to the preconceptions of those skilled in the art, the present invention affords not only the possibility of significant cost savings, but also dramatically increased reliability.